The second beta of Apple's iOS 5.0 mobile operating system began making its way to developers on Friday, revealing cosmetic changes to certain lock-screen notifications, a slide away keyboard in iMessage, and other tweaks.

Apple unveiled a new iMessaging app that brings SMS-style messaging to iOS devices that lack a mobile data connection, such as WiFi-only iPads and the iPod touch. The technology behind the software presents several advantages for mobile devices over offerings from rival Google and Microsoft, and is also likely to soon find its way to iChat on Mac.

When it's released by Apple this fall, iOS 5 will bring an improved Web browsing experience to iPhone and iPad users, offering new features in Safari like private browsing, Reader, and tabs on the iPad.